1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor device and a substrate processing apparatus in which a thin film is formed on a substrate.
2. Description of the Related Art
As one of manufacturing steps of a semiconductor, there is a CVD (Chemical Vapor Deposition) step in which a predetermined film-forming process is preformed on a surface of a substrate (a substrate to be processed based on a silicon wafer, glass, or the like, on which a fine electric circuit pattern is formed). In this step, the substrate is mounted in an airtight reaction chamber and heated by a beater provided in the chamber, and chemical reaction is caused while introducing a source gas to the substrate so as to form a thin film evenly on the fine electric circuit pattern formed on the substrate. In this reaction chamber, a thin film is also formed on components other than the substrate. A CVD apparatus shown in FIG. 10 is provided with a showerhead 6 and a susceptor 2 in the reaction chamber 1, and the substrate 4 is mounted on the susceptor 2. The source gas is introduced into the reaction chamber 1 through a source gas supply pipe 5 connected to the showerhead 6 and supplied onto the substrate 4 via many holes 8 provided on the showerhead 6. The gas supplied to the substrate 4 is exhausted through an exhaust pipe 7. Incidentally, the substrate 4 is heated by a heater 3 provided under the susceptor 2.
As such a CVD apparatus, there exists a CVD apparatus in use of a MOCVD (Metal Organic Chemical Vapor Deposition) method in which an amorphous HfO2 film and an amorphous Hf silicate film can be formed by using an organic chemical material as a film-forming source.
For the film-forming source, Hf[OC(CH3)3]4 (It is referred to as Hf-(OtBu)4 below), Hf[OC(CH3)2CH2OCH3]4 (It is referred to as Hf-(MMP)4 below. Note that MMP indicates 1 methoxy-2-methyl-2-propoxy), Hf[O—Si—(CH3)3]4 (It is referred to as Hf—(OSi)4), and the like are used.
In these chemicals, many organic materials, for example, such as Hf-(OtBu)4 and Hf-(MMP)4, are in liquid phase at normal temperatures and pressures. Therefore, Hf-(MMP)4, for example, is utilized after changed into gas at vapor pressure by heating.
Incidentally, there is a problem that it is difficult for the thin film deposited by the aforementioned MOCVD method to obtain flatness of the film surface. Particularly, the problem described above becomes remarkable in the MOVCD method in which the deposition rate of the thin film is determined by the surface-reaction rate controlling. It is known that there occurs a time lag for the thin film to start deposition on the surface of the substrate in the surface-reaction rate controlling. This time is called incubation time. It is considered that a nucleation process in which deposition in island shape is performed on the substrate occurs during this incubation time and that the flatness of the thin film is lost by formation of irregularities in this nucleation process.
A conceptual view of the irregularities on a thin film 31 formed on the substrate 4 is shown in FIG. 7. It is assumed that a projecting part 33 on the surface 32 of the thin film is formed during the nucleation process. Difference between the maximum value of the projecting part 33 and the minimum value of a concave part 34 indicates height difference H in the irregularities, and this difference H is called flatness, showing that the flatness is inferior when the difference is large and the flatness is superior when the difference is small.
A conceptual view of generation of a nucleus (formation of an island) which is assumed to occur during the incubation time is shown in FIG. 8. The foundation of the formed film is the silicon substrate 4, the silicon substrate 4 with an SiO2 film thinly applied on the surface thereof, or the silicon substrate 4 with a Si3N4 film applied on the surface thereof. A nucleus 35 is formed on the surface of the substrate or on the surface of the foundation film 30. This nucleus 35 grows to be a thin film. At this time, while a film tends to adhere to the nucleus 35 easily, the film tends not to adhere to the surface of the substrate or to the surface of the foundation film 30 easily on which the nucleus 35 is not formed. Therefore, it is difficult for the thin film deposited by the MOCVD method to obtain flatness of the surface of the thin film 32 as shown in FIG. 7.
This flatness of the surface of the thin film 32 is a factor to lower the reliability of the semiconductor device which is an end product and produces a big problem with downsizing of the device.
Following publications are disclosed as publicly known examples of a conventional film-forming technique in use of CVD.
(1) Japanese Patent Laid-opened No. Hei 9-82696 (publicly known example 1)
The publicly known example 1 is a method for forming a silicon oxide film having a desired film thickness by repeating a condensed film forming process (first step), in which an oxygen radical and an organic silane gas (TEOS) are supplied concurrently at a low temperature (−50 to +50° C.) to form a condensed film of a silicon oxide film by a condensed CVD method, and a modifying process (second step), in which the temperature of the substrate is set high (400° C. to 600° C.) thereafter while the oxygen radical is kept supplied and the condensed film is thermally processed in an oxygen radical atmosphere to be modified (removal of impurities such as C, H, and the like), more than once in the same reaction chamber. A thinner film than a film which is to be formed finally is formed in the first step and the condensed film is modified in the second step, whereby the impurities such as C, H, and the like can be removed evenly.
(2) Japanese Patent Laid-opened No. 2001-68485 (publicly known example 2)
The publicly known example 2 is a method which includes steps of growing a low temperature growth ZnO layer by concurrently radiating a Zn beam and an oxygen radical beam onto a sapphire substrate at a temperature lower than a single crystal ZnO growth temperature (200 to 600° C.) (first step), thermally processing (flattening processing) the low temperature growth ZnO layer at a temperature (600 to 800° C.) higher than the growth temperature of the low temperature growth ZnO layer while radiating the oxygen radical beam (second step), and growing a high temperature growth single crystal ZnO layer on the low temperature growth ZnO layer by concurrently radiating the Zn beam and the oxygen radical beam at 600 to 800° C. (third step). Superior crystallinity is made in such a manner that the low temperature growth ZnO layer which is formed in the first step is flattened in the second step and then the high temperature growth single crystal ZnO layer is grown in the third step.
(3) Japanese Patent Laid-open No. Hei 6-45322 (publicly known example 3)
In a manufacturing method of a SiN film of the publicly known example 3, a natural oxide film on a surface of a poly-Si film is removed by hydrogen annealing and thereafter a substrate is transferred into a vapor-phase growth furnace of a heat lamp system without being exposed to the air. After the substrate is transferred, SiH2Cl2 gas and NH3 gas are concurrently supplied onto the poly-Si film at a low temperature (700° C.) to form a first SiN film having a first film thickness (5 angstroms) (first step), and after raising the temperature (700→800° C.), the SiH2Cl2 gas and the NH3 gas are concurrently supplied to form on the first SiN film a second SiN film having a second film thickness (100 angstroms) which is larger than the first film thickness (second step). Since growth at the low temperature in the first step enhances surface density of a growing nucleus and realizes a film having a superior flatness, it is possible to form a SiN film having a desired film thickness in the second step.
(Patent Document 1)
Japanese Patent Laid-open No. Hei 9-82696 (pages 2 to 9, FIG. 1)
(Patent Document 2)
Japanese Patent Laid-open No. 2001-68485 (pages 2 to 4, FIG. 1)
(Patent Document 3)
Japanese Patent Laid-open No. Hei 6-45322 (pages 2 to 4, FIG. 1)
However, there are following problems in the above-described publicly known examples.
(1) In the publicly known examples 1 and 2, the source gas and the radical are concurrently supplied in the first step (low temperature process). However, since the oxygen radical is highly reactive, particles are generated when the source gas and the oxygen radical are supplied concurrently.
(2) In the film-forming methods such as publicly known examples 1 to 3, which include the second step at the high temperature after the first step at the low temperature, the throughput (productivity) is lowered because the temperature of the substrate is needed to be raised after the first step at the low temperature.
Incidentally, both of the first layer and the second layer (and layers formed thereafter) are formed by the CVD method in the publicly known examples 1 and 3, and both of the first layer and the second layer are formed by an MBE method in the publicly known example 2.